Writing instrument



FIG. 1 is a front perspective view of a writing instrument showing my design;

FIG. 2 is a bottom plan view;

FIG. 3 is a front elevational view, the rear view being a mirror image thereof;

FIG. 4 is a right side elevational view, the left side being a mirror image thereof; and,

FIG. 5 is a top plan view thereof. 

The ornamental design for a writing instrument, as shown and described. 